Wang R, Li X A
Department of Radiation Oncology, University of Maryland, Baltimore 21201, USA.
Med Phys. 2001 Aug;28(8):1776-85. doi: 10.1118/1.1388222.
In this work, we have calculated the two-dimensional dose distribution in water for a 32P intravascular brachytherapy source wire using the EGSnrc Monte Carlo code. The beta source (Guidant Vascular Intervention) has a radioactive core with a length of 27 mm and a diameter of 0.24 mm. The dose parameters required by the AAPM TG-60 formalism are discussed and calculated. Dose rate evaluated at the reference point is 0.1311+/-0.0001 Gy min(-1) mCi(-1). For the beta source studied, the dose distribution is uniform along the axial direction z for a given radial position p for - 10 mm< or =z< or =10 mm and p< or =7 mm. In such a dose-uniformity region, the dose field can be characterized by one-dimensional dose distribution, D(p), the dose distribution on the transverse axis. Beyond this region a two-dimensional (2D) description is necessary. However, for the long beta source wire the anisotropy function proposed by the TG-60 formalism becomes indefinable when the radial distance exceeds penetration depth of beta electrons. We have proposed that the anisotropy function be expressed in the cylindrical coordinate system, instead of a polar system, to remedy this deficiency. For practical purposes, the entire 2D dose distribution and the dose parameters calculated in the work are tabulated for ease of use.
在这项工作中，我们使用EGSnrc蒙特卡罗代码计算了用于32P血管内近距离放射治疗源线在水中的二维剂量分布。β源（Guidant血管介入公司生产）有一个放射性芯，长度为27毫米，直径为0.24毫米。讨论并计算了美国医学物理师协会（AAPM）TG - 60形式主义所需的剂量参数。在参考点评估的剂量率为0.1311±0.0001 Gy min(-1) mCi(-1)。对于所研究的β源，在-10毫米≤z≤10毫米且p≤7毫米的情况下，对于给定的径向位置p，剂量分布沿轴向z是均匀的。在这样的剂量均匀区域，剂量场可以用一维剂量分布D(p)来表征，即横轴上的剂量分布。超出该区域则需要二维（2D）描述。然而，对于长β源线，当径向距离超过β电子的穿透深度时，TG - 60形式主义提出的各向异性函数变得无法定义。我们提议在柱坐标系而非极坐标系中表达各向异性函数，以弥补这一不足。出于实际目的，将工作中计算的整个二维剂量分布和剂量参数制成表格以便于使用。
